1. Field of the Invention
The present invention relates to apparatus for measuring distance between points on an object or objects that are spaced from one another, in general, and to such apparatus for measuring the distance between a coating applicator and a backing roller physically spaced from said applicator, in particular.
2. Description of the Prior Art
In the operation of present-day coating apparatus where coatings of critical thickness are desired to be deposited on a substrate such as a moving web for use in photographic film, it is necessary to precisely control the gap or distance between the coating applicator and the substrate onto which said coating is deposited by said applicator in order to control coating thickness. This gap dimension is normally controlled by controlling the distance between the coating applicator and said web or between the coating applicator and a coating or backing roller, a device that supports the web and transports same to said applicator for coating.
Coating applicators are frequently removed from coating apparatus for any number of reasons, the most common one being for applicator cleaning. If the applicator is removed from the coating apparatus for an excessive period of time, web coating production will be adversely affected. In order to minimize the down time or the time that the coating apparatus is not applying a coating to a moving web and the attendant lost production, it is essential that that applicator be returned to its precise web-coating position as soon as possible.
The present method for establishing the desired spacing between a coating applicator and a backing roller for a moving web involves placing one or more shims or feeler gauges of the appropriate thickness at several spaced-apart positions between the applicator and the backing roller while the applicator is in a movable condition and the backing roller mountings are mounted in a fixed position. Once the desired spacing has been established, the applicator is clamped in a fixed position.
One applicator-to-backing roller measurement technique involves plastic shim stock or feeler gauges and a touch sensitive to looseness and tightness of fit. More accurate steel feeler gauges cannot be used because they damage applicators and rollers.
The use of plastic feeler gauges to establish the proper applicator-to-backing roller gap has several disadvantages. Feeler gauges are available in limited sizes and it is often necessary to make sandwiches of several feeler gauges. Feeler gauges buckle readily, especially those that are extremely thin. The thinnest useable feeler guage is 1.0 mil and therefore the effective resolution with such a gauge is approximately 0.5 mil. Also, different people get different results because of their different sensitivity to looseness and tightness of fit.
While the use of feeler gauges will result in the spacing of an applicator from its associated moving web backing roller to within acceptable tolerances, in addition to the disadvantages noted above, this method consumes a disproportionate share of coating apparatus down time when, for example, the applicator is removed for cleaning.
An object of the present invention is to provide apparatus for rapidly and more accurately establishing the proper spacing between objects that are spaced apart from one another.